1. Field of the Invention
The present invention relates to a vibrating body for a vibratory drive unit called a vibration wave actuator or the like, and a vibratory drive unit, and more particularly, to a vibrating body for a vibratory drive unit in which piezoelectric elements are provided respectively on front and back surfaces of a plate-shaped elastic member.
2. Description of the Related Art
Conventionally, in a vibratory drive unit (vibration wave actuator), a piezoelectric element is generally used as a vibration source for a vibrating body.
FIG. 8 is an outer perspective view of a vibratory drive unit 70 according to Japanese Patent Application Laid-Open No. 2004-304887.
The linear vibration wave actuator 70 includes a vibrating body 71 and a linear slider 76 that is brought into pressure contact with the vibrating body 71.
The vibrating body 71 includes a piezoelectric element 75 and a drive plate 72, and the piezoelectric element 75 is a laminated piezoelectric element in which multiple piezoelectric layers and multiple electrode layers are laminated alternately. The drive plate 72 is made of metal and is bonded to the piezoelectric element 75 with an adhesive.
The drive plate 72 has a plate portion formed in a rectangular shape and two protrusions 73 formed in a convex shape on the upper surface of the plate portion.
The tip surface of the protrusion 73 is a member to be brought into direct contact with the linear slider 76 that is a body to be driven, and hence, has abrasion resistance.
The vibrating body 71 of the linear vibration wave actuator 70 excites two bending vibration modes.
FIGS. 9A and 9B illustrate the two bending vibration modes.
As illustrated in FIG. 9A, one of the bending vibration modes is a secondary bending vibration in the long-side direction (X-direction) of the vibrating body 71, which has three nodes parallel to the short-side direction (Y-direction). Here, the protrusions 73 are each placed close to the position to be a node.
As illustrated in FIG. 9B, the other of the bending vibration modes is a primary bending vibration in the short-side direction (Y-direction) of the vibrating body 71, which has two nodes parallel to the long-side direction (X-direction). Then, the protrusions 73 are each placed close to the position to be an antinode of the primary bending vibration.
The two bending vibration modes are excited to generate an elliptic motion in the two protrusions 73. As illustrated in FIG. 8, the elliptic motion generates a relative locomotion power between the vibrating body 71 and the linear slider 76 that is in pressure contact with the vibrating body 71.
The relative locomotion power can drive the linear slider 76 linearly.
Further, the configuration illustrated in FIGS. 10A to 10C is a vibrating body 80 in a vibration wave actuator according to Japanese Patent Application Laid-Open No. 2009-124791.
The vibrating body 80 is assumed to be applied to the above-mentioned linear vibration wave actuator.
The vibrating body 80 includes a piezoelectric element 81 that is a vibration source and a ceramics substrate 82 that is a plate-shaped elastic member which vibrates integrally with the piezoelectric element 81.
The ceramics substrate 82 and the piezoelectric element 81 are integrally bonded (fixed) to each other by calcination. In addition, the piezoelectric element 81 is sintered.
In the piezoelectric element 81, a piezoelectric layer 83, an electrode layer 84, a piezoelectric layer 85, an electrode layer 86, and a piezoelectric layer 87 are laminated successively on one surface of the ceramics substrate 82 that is an elastic member.
The electrode layers 84 and 86 are placed so as to be divided into two parts, and the piezoelectric layers 85 which are divided into two parts and sandwiched between the electrode layers 84 and 86 are polarized after calcination. As a result, the above-mentioned two bending vibration modes can be excited by applying an AC voltage to the piezoelectric layers 85 divided into two parts.
In the vibratory drive unit as described in Japanese Patent Application Laid-Open No. 2004-304887 illustrated in FIG. 8, the laminated piezoelectric element and the drive plate (elastic member) made of metal are bonded to each other with an adhesive made of resin.
However, the adhesive is relatively soft, and hence, particularly when the temperature increases due to the drive, the adhesive becomes softer. Therefore, the influence on vibration attenuation of the vibrating body is large, which is a main factor for degrading the efficiency of the vibratory drive unit.
Further, when the vibratory drive unit is downsized, a fluctuation in thickness of an adhesive layer of an adhesive and the position precision relating to bonding more affect the performance of the downsized vibratory drive unit, which also increases the fluctuation in performance.
Further, the conventional piezoelectric element is produced independently through a large number of steps such as the formation from piezoelectric material powder, the calcination, and the subsequent mechanical processing and attachment of electrodes, which is one factor for increasing production cost.
To address the problem, the vibrating body according to Japanese Patent Application Laid-Open No. 2009-124791 has been devised, in which a piezoelectric element is directly bonded to an elastic member without using an adhesive, at the same time as the production of the piezoelectric element.
However, in the case of providing the piezoelectric element only on one surface of a ceramics substrate that is an elastic member, the elastic member is warped and deformed due to the contraction of the piezoelectric element during calcination.
Further, for a higher output which leads to the downsizing of the vibrating body, the output is small only with the piezoelectric element provided only on one surface. Therefore, it is desired that the piezoelectric element have a multi-layered structure, but there is a problem that the multi-layered structure only on one surface causes large warpage deformation.